1. Field of Invention
The present invention relates to a filter device and more particularly to a hollow fiber filter device used to filter, for example, return water (condensate recycled) in a nuclear power plant.
2. Description of the Related Art
In the conventional hollow fiber module for use in a filter, a plurality of hollow fibers are formed in a bundle and an upper end of the bundle is secured to a horizontal plate within the filter casing so that each fiber is open at the upper end while being closed at the lower end with a filling material inserted at that end or with two opposite ends thereof being open and positioned at the upper portion in such a manner that the overall configuration thereof is U-shaped. Thus, the construction of such a module has been made by securing one end of the bundle to a solid member while leaving the opposite end free so that the module may be handled by such solid member.
Therefore, such a module consisting of fine fibers having, for example, a small diameter of 0.4-1 mm tends to be rather flexible and easily damaged. Furthermore, it is also easily entangled due to vibration imposed thereon when it is subjected to backwashing which is usually accompanied with air bubbles. Also, it has been noticed in the hollow fiber filter module that filtering through the wall of the hollow fiber has not been uniform on the outside of the bundle and the inside of the bundle, particularly when the diameter of the bundle of hollow fibers is large.